There is a need in some millimeter wave/microwave devices of low temperature coefficient permanent magnet materials in which the temperature coefficient is low enough such that the variation of remanent magnetization is less than 2 percent over the temperature range of -50 degrees C. to +150 degrees C. The current commercially available SmCo.sub.5 based magnets have a rather high reversible temperature coefficient (RTC) of magnetization of 0.044 percent/C.
There has recently been reported a Sm.sub.2 Co.sub.17 -based alloy having an improved energy product as compared to SmCo.sub.5 based compounds. The alloy has the composition Sm.sub.2 Cu.sub.1.6 Zr.sub.0.16 Fe.sub.3.3 Co.sub.12. Though the alloy has an improved energy product, its reversible temperature coefficient of magnetization is too high.